To determine what type of Box account you will need review type and volume of calls expected to be made to / from the numbers / trunks you will enable call recording for. To assist you:

the size of a call, whilst dependent on the quality of the call (that is, the CODEC being used) is approximately 1.8 Mb per one minute of two-way conversation

therefore a 10 Gb account will provide over 90 hours of calls

please note that Box accounts, especially free/personal accounts, may have additional restrictions such as no single file being greater than 250 Mb in size (therefore no call exceeds circa. 2 hours 15 minutes)

Note that all Box accounts, including the entry level free/personal accounts, are capable of storing SIP Trunk Plus calls.